1. LIGO-G0900550-v4 Advanced Interferometers and their Science Reach David Shoemaker, MIT – LIGO Amaldi, June 2009 – Columbia University

2. LIGO-G0900550-v4 The next phase Initial instruments worked remarkably well »Delivered the instrument science »Established the infrastructure »Reached their design sensitivities »Developed the paradigms for data analysis »Did real astrophysics – provided new upper limits, made important non-detections …but they have not (yet) detected gravitational waves »Some analyses of existing high-sensitivity data not yet complete »May still find a gem in the rough! Community impatient to move to frequent detections, use of GWs as an observing tool What’s needed? 2

3. LIGO-G0900550-v4 Advanced Detector goals 3 10 8 ly Enhanced LIGO/Virgo+Virgo/LIGO Credit: R.Powell, B.Berger Adv. Virgo/Adv. LIGO/LCGT A factor of ~10 improvement in linear strain sensitivity over the initial instruments »Just about at the current practical limit of instrument science »A nice round number (if we had 12 fingers, we’d do a bit better yet) Corresponds to Strain sensitivity h of ~3x10 -23 in a 100 Hz bandwidth By itself, brings ~10 3 more candidates into reach Can also push down in frequency, say to 10 or 20 Hz …and, quite importantly, growing the network »Extracting polarization, position »Increasing uptime, SNR Losurdo

4. LIGO-G0900550-v4 A tour of the challenges and innovations What are the limits to performance and the concepts for addressing them? What solutions have been adopted for the ‘Advanced’ detectors – and their immediate predecessors, the ‘enhanced’ or ‘+’ versions? s4

5. LIGO-G0900550-v4 Introduction to the Characters: Virgo+: a 3km-arm 1.5 generation instrument, testing and exploiting 2 nd generation approaches Enhanced LIGO: two 4km-arm 1.5 generation instruments, testing and exploiting 2 nd generation approaches Advanced Virgo: a 3km-arm 2 nd generation instrument, developed by the Virgo collaboration and EGO, sited in Cascina, Italy Advanced LIGO: three 4km-arm 2 nd generation instruments, developed by the LIGO Scientific Collaboration, sited at Hanford, Washington and Livingston, Louisiana USA. GEO-HF: a 600m-arm 2+ nd generation instrument, developed by the GEO collaboration, sited near Hannover, Germany LCGT: a 3km-arm 2+ nd generation instrument, developed by a Japanese consortium, underground at Kamioka, Japan ACIGA – potential for a multi-km system in Australia on 2 nd - generation time scales 5

6. LIGO-G0900550-v4 Some challenges: Seismic Noise An obvious way to mask gravitational waves: seismic noise »Noise spectrum grows rapidly toward low frequencies --- requires something like 9 orders of magnitude of suppression at 10 Hz All instruments using a pendulum suspension of the optic, one or more layers, to give final isolation (more later) Most instruments using initial instrument approach: multiple passive pendulums in series »Prime Example: Virgo ‘Superattenuator’ to serve for the Advanced Virgo instrument »Virgo+, AdvVirgo, LCGT also use this approach »Masses and springs, similar in principle: GEO-HF 6 Losurdo

7. LIGO-G0900550-v4 Active seismic isolation One new approach is ‘active’ suppression, used in Advanced LIGO »Low-noise seismometers on payload detect motion in all six degrees-of-freedom »Actuators push on payload to eliminated perceived motion »Multiple 6-DOF stages to achieve desired suppression, allocation of control Challenges in structural resonances, sensor performance Nice to have a quiet table to mount lots of stuff on Enhanced LIGO using this approach for one chamber per interferometer »Meets requirements, will remain in place for AdvLIGO 7 Leaf springs Intermediate stage base Sensors – Actuators Lantz-Giaime x1000 Optics table

8. LIGO-G0900550-v4 Newtownian background Fluctuations in the local gravity gradient Test mass can’t distinguish from GWs Starts to limit Advanced detectors ~15 Hz Could put down an array of seismometers, try to regress out the background… Or move underground »Reduced level of seismic activity »Symmetrization of earth-air interface LCGT to be placed next to Kamiokande, 1000 m underground Many orders of magnitude quieter – due to simple seismic noise reduction, and ~1 order quieter in gradients 8 Mandic Kuroda Surface motion Underground

9. LIGO-G0900550-v4 9 Mandic Newtownian background Fluctuations in the local gravity gradient Test mass can’t distinguish from GWs Starts to limit Advanced detectors ~15 Hz Could put down an array of seismometers, try to regress out the background… Or move underground »Reduced level of seismic activity »Symmetrization of earth-air interface LCGT to be placed next to Kamiokande, 1000 m underground Many orders of magnitude quieter – due to simple seismic noise reduction, and ~1 order quieter in gradients 9 Mandic Kuroda Surface motion Underground

10. LIGO-G0900550-v4 Test mass isolation and control Test mass suspension complements seismic isolation All instruments using several pendulums in series for improved isolation, staging of control forces and dynamic range Glasgow has championed multiple-stage pendulums, and UK Consortium has designed and is fabricating suspensions for Advanced LIGO »4 stages; sensors and actuators as needed to manage forces and dynamic range Combined attenuation of seismic noise ~10 orders of magnitude at 10 Hz 10 10 -5 10 -20 m/rHz 10 -15 10 -10 1 Hz0.110 Robertson

11. LIGO-G0900550-v4 Suspension Thermal Noise ½ kT of energy in each mode, expressed according to the Fluctuation-Dissipation theorem Managed by »gathering noise power into a narrow band around suspension resonances, via… »Use of very high quality factor (low loss) materials, »push fundamental resonances below observation band Fused Silica suspension fibers, as pioneered by GEO (Glasgow) in the GEO600 instrument »Advanced LIGO: as the final stage of suspensions delivered by the UK consortium »In Advanced Virgo, using somewhat different connection approaches, same principle »In Virgo+ -- as early as late 2009/early 2010 11 Harry Robertson

12. LIGO-G0900550-v4 Suspension thermal noise ½ kT…suppose we lower the temperature? (thermal noise scales as √T) Sapphire suspension fibers, pioneered by the Japanese consortium/ICRR, planned for LCGT, motivated by cryogenic cooling of suspension and mirrors High thermal conductivity, to draw heat from test mass deposited by laser beam Mechanical losses decrease as temperature drops – some cancellation of noise sources Challenges in quiet refrigeration confronted An important candidate for 3 rd generation instruments 12 Kuroda

13. LIGO-G0900550-v4 Test Mass and Coating thermal noise Again, thermal energy of mechanical modes of the optic substrate which serves as the test mass cause motions of surface LCGT paving the way for 3 rd generation instruments with a cryogenically cooled sapphire mirror – lowering noise by sqrt(T) Most instruments using fused silica as the substrate material as for initial instruments »Virgo+, AdvVirgo, eLIGO, AdvLIGO, GEO600 »Loss values of ~10 -8 … »Substrate thermal noise not a problem Mirror coatings: loss values of ~10 -4 THE dominant mid-range noise Meets 10x improvement, barely Continuing work well rewarded! 13 M. Evans

14. LIGO-G0900550-v4 Laser light sources Need order of ~150-200W to achieve Advanced sensitivities GEO-HF, Adv LIGO, LCGT -- 150-200W Nd-Yag lasers »Max Planck Hannover-developed solution for the laser for several projects »modulators, isolators, thermal compensation schemes are advanced for a factor ten eLIGO – 35W front end laser »Starting to see success in using this light! Adv Virgo – keeping option of a fiber laser open »Valuable path to explore for 3 rd generation instruments 14

15. LIGO-G0900550-v4 Strain sensing approach Adv Virgo, AdvLIGO, LCGT – signal recycling, Pioneered in GEO600 Allows some tuning, used to balance technical limitations and astrophysical signatures GEO-HF – will use squeezed light »Can achieve e.g., same sensitivity for less light power »pathfinding for 3rd Generation (or 2.5 or 2.3….) »May test in LIGO/eLIGO/AdvLIGO… 15 Signal recycling mirror Kawamura

16. LIGO-G0900550-v4 And hardware exists! 16

17. LIGO-G0900550-v4 x1000 1 st gen 2 nd gen Kopparapu via Mandel A bit on the astrophysical targets: Neutron-star binary coalescence 17 The source for which we have the best templates, and now also an idea of the coalescence/ ringdown… …and the best rate estimates. Advanced detector rates are likely to be 40 /year but still uncertain to a factor 10 in either direction Rates for other species less sure »NS-BH – best guess 10 /year »BHBH – best guess 20 /year Scheel et alia Shibata et alia

18. LIGO-G0900550-v4 Ando et al. Supernovae (one example of a ‘burst’ source) Know of ~1-3 per year out to the Virgo cluster Advanced detectors can see ~10 -6 M s out to 1 Mpc -- ~1/150 yr But some proposed mechanisms release more energy than this, and May be more that we do not yet see Great target for multi-messenger astrophysics with neutrinos – increases reach and confidence 18

19. LIGO-G0900550-v4 Periodic sources Pulsars will emit GWs if asymmetric; lots of discussion about the stiffness of the shell One mechanism for Low-mass X-ray binaries: GW emission (due to “mountains”) balances long-term accretion torque Handful of known pulsars appear to be in reach for a 2-year observation Will continue all-sky search using Einstein@home screen-saver approach 19 Watts via Chakrabarty

20. LIGO-G0900550-v4 Stochastic sources Have already ‘beat’ the Big-Bang nucleosynthesis upper limit Huge increase in sensitivity for the AdvLIGO pair despite overlap function – due to improvement in low-frequency sensitivity Standard inflationary models out of reach for 2 nd gen detectors… have to wait for 3 rd gen or space! But some Cosmic String models, defects, etc. can be tested …and surprises to be found 20

21. LIGO-G0900550-v4 Surprises Broad sensitivity of the Advanced detectors, multiple detectors for confidence and coverage, and the sheer number of candidate systems convinces me we will see lots of signals! 21

22. LIGO-G0900550-v4 The Network 22 Network sensitivity For 50% Sensitivity Coverage LIGO LIGO+Virgo LIGO+Virgo+LCGT Schutz

23. LIGO-G0900550-v4 So…. There is a range of nice new technologies which appear to be able to deliver the desired 10x sensitivity, <1000x volume There are a number of sources waiting to be detected eLIGO and Virgo+ will start observing with some enhanced sensitivity this summer – and with many parts of Advanced Instruments being explored, exploited, refined ACIGA, other groups, establishing plans for instruments Advanced Virgo plans a start this summer, LCGT also has optimism for a start in the near future …not just plans: The Advanced LIGO Project is underway since April 2008 (Thank you, NSF!) 2015 will be a very good year! 23